The Japanese, who embarrassed the Chinese on the opening day of the Games on Sunday by winning the event's first gold medal in the women's marathon, were poised to win three of five gold up for grabs in the pool today.

With Japan's men swimmers at least the equal of the Chinese, the title is expected to be decided by how well the women of the rising sun perform.

``Chen Yan is not in good health,'' team manager Zhang Xong said. ``She has not been in good form recently -- but she will race again here.''

Yesterday, Chen came third in the 4x100 individual medley, an event in which she is the world champion and record holder.

She lifted the 400m freestyle title at the World Championships in Perth in January and was among the favourites for the 200m freestyle gold in Bangkok.

Other heats set up some intriguing China-Japanclashes for today's five finals.

Fastest qualifier for the women's 200m freestyle was Sachiko Yamada of Japan, ahead of China's Qin Caini.

Japan's Takashi Yamamoto headed the qualifiers for the men's 100m butterfly in 54.20 seconds, less than half a second off the games record set by Jiang Chengli of China in Hiroshima four years ago.

China's Qi Hui set the pace in the women's 200m breastroke, qualifying fastest ahead of Japan's Masami Tanaka and South Korean Kye Yoon-Hee in a tight second heat.

South Korea qualified fastest for the men's 4x200 freestyle relay, ahead of Singapore, China and Japan.

In a day that saw lacklustre performances from the once invincible Chinese team, Xiong Guoming, a 1994 Games winner who lost his gold medal after a dope test, qualified only sixth fastest in the men's 4x100 individual medley.

The fastest qualifier was Takahiro Mori of Japan, in four minutes 23.34 seconds.

Ailing Chen withdraws: Chinese double world champion Chan Yan pulled out of the women's200m freestyle at the Asian Games today, opening the door for Japan's Sachiko Yamada who led the qualifiers for the final.

Chen, the 400m medley world record holder who had to battle for bronze in her speciality event Monday, didn't start her heat for the 200m freestyle.

Chinese coach Han Mingyan said the 17-year-old was weak after suffering from diarrhoea the previous night. ``We sent her to the village clinic this morning. As she is rather weak now, whether she will continue to compete in the games is still in doubt, not to say winning gold.''

But Chinese head coach Zhang Xiong said chen will enter women's 200m individual medley, in which she won a silver at Perth. ``I'm sure she'll take part in that event,'' he said.

Chen was also scheduled to swim the 400m freestyle, in which she won gold in Perth. Her poor form was a good news to Japan. ``The mediocre form plaguing Chen will give us more chances to win,'' said Japanese team leader Tsuyoshi Aoki.

Yamada topped the qualifiers in women's 200mfreestyle, while fellow Japanese Takashi Yamamoto qualified first in men's 100m butterfly.

Diving grace: World Championship silver medalist Guo Jingjing easily won the women's three metre springboard gold at the Asian Games, leading a Chinese double triumph.

Guo amassed 547.47 points to beat compartriot Yang Lan, who took silverwi